BE1030111B1 - METHOD FOR IMPREGNING WOOD - Google Patents

Abstract

The present invention relates to a method for treating wood, more specifically a method in which wood is treated by pressure impregnation with wood preservatives. Furthermore, the invention relates to wood treated according to the method of the present invention.

Description

! BE2021/6069

METHOD FOR IMPREGNING WOOD

TECHNICAL DOMAIN

The present invention relates to a method of treating wood, more specifically to a method in which wood is treated by impregnation with wood preservatives.

STATE OF TECHNOLOGY

Organic materials such as wood are sensitive to rotting processes under the influence of penetrating moisture. As a result, many types of wood are not suitable for long-term outdoor use if they are unprotected and the growth of wood-degrading micro-organisms is possible.

One way to protect wood is to lower the moisture content in the wood sufficiently, usually below 12%, so that the growth of wood-destroying micro-organisms is no longer possible. Subsequently, coating or superficial impregnation with wax, paint and the like prevents the wood from absorbing moisture again. Another possibility to protect wood against rotting is to impregnate it (after drying) with biocides. Wood can also be impregnated with chemical reagents that chemically modify or crosslink the wood, making it more stable and less susceptible to rotting, such as BASF's Belmadur® technology.

A common problem with impregnation is that parts that are not reached during the impregnation process can still rot if moisture penetrates. Impregnation can be done by the capillary suction of wood, but this is time consuming and not reliable. A better way of impregnating wood is under pressure.

Methods for impregnating wood under pressure are known in the art. The methods used in industry mainly exist in two variants.

The first is the empty cell method which consists of three steps. In a first step, the pre-dried wood is placed under high pressure in an airtight sealable room or autoclave and kept there. The duration of this step depends on the

2 BE2021/6069 wood type and is between half an hour and an hour. In a second step, the air in the room is replaced by the wood preservative while the pressure in the room is kept constantly high. Once the space around the wood has been filled with wood preservative, the pressure is further increased and maintained for a certain time, depending on how much wood preservative needs to be absorbed by the wood. In the third step, the wood preservative that has not been absorbed is removed by applying a vacuum.

The second method is the full cell method (Bethel method) and consists of the following steps. In a first step, the pre-dried wood is placed under vacuum in an airtight sealable room or autoclave to remove as much air and residual water as possible from the wood (the pre-vacuum). In a second step, the wood preservative is placed in the autoclave until the wood is submerged.

In a third step, the pressure is increased and the high pressure is maintained for a certain time, depending on how much wood preservative has to be absorbed by the wood. In the fourth step, the wood preservative that has not been absorbed is removed by applying a vacuum (the post-vacuum).

WO 1998/018872 A1 describes a method for treating wood with silicates. In addition, after an optional vacuum phase, the wood is impregnated under pressure with a sodium silicate and borax solution, supplemented with surfactants and rheological modifiers necessary for good impregnation. After releasing the pressure, removing the wood preservative, and optionally an additional vacuum phase, the wood is dried.

WO 2004/113039 A1 describes a method in which, after applying a pre-vacuum, the impregnation step at elevated pressure is already interrupted after a few minutes before maximum absorption of the wood preservative is achieved, so that the residual vacuum still removes the superficially present wood preservative. absorbed by the wood. This prevents dripping of wood preservative from the treated wood.

No post-vacuum is applied.

To improve the penetration of the wood preservative into the wood, the wood and/or wood preservative is sometimes heated.

3 BE2021/6069

WO 2009/040656 A2 describes a method in which, after applying a pre-vacuum, the wood is impregnated with the protective agent under pressure. Optionally, the wood is heated via electromagnetic radiation by means of electrodes placed between the wood, either before the protective agent is brought to the wood, or afterwards.

WO 2019/185098 A1 describes a method in which, after applying a pre-vacuum, the temperature of the medium is raised to 220°C during the impregnation at elevated pressure and the wood is subjected to ultrasonic sound.

However, the disadvantages of the additional thermal and physical stress are that the properties of the wood can be negatively influenced and the wood preservative can be affected. Moreover, these methods are less interesting both ecologically and economically.

The object of the invention is to provide a method for efficient absorption of any wood preservative by wood without the adverse effects of a high treatment temperature or too high a treatment pressure.

The inventors found through experimentation that by the proper application of a pre-vacuum, an overpressure, and a post-vacuum, where the pre-vacuum is maintained until the filling of the autoclave is complete, a high impregnation efficiency is possible without heating of the the wood and/or wood preservative is required.

SUMMARY OF THE INVENTION

In a first aspect, the invention relates to a method for impregnating wood with a wood preservative, comprising: (1) placing the wood to be impregnated in an autoclave, (ii) applying a pre-vacuum with negative pressure between -600 and -1000 mbar, preferably between -700 and -1000 mbar, more preferably between -800 and -1000 mbar, even more preferably between -850 and -1000 mbar, and even more preferably between -850 and -950 mbar, during at least 5 minutes, preferably at least 10 minutes, more preferably at least 15 minutes, even more preferably at least 20 minutes, and even more preferably at least 30 minutes,

4 BE2021/6069 (iii) filling the autoclave under negative pressure with a solution of wood preservative, whereby the negative pressure is maintained, (iv) increasing the pressure and maintaining overpressure in the aforementioned space to at least 10000 mbar, preferably at least 11000 mbar, more preferably at least 11500 mbar, even more preferably at least 12000 mbar, even more preferably at least 12500 mbar, most preferably between 12500 and 13000 mbar, for at least 30 minutes, preferably at least 60 minutes, more preferably at least 90 minutes, even more preferably at least 120 minutes, and even more preferably at least 180 minutes, (v) reducing the pressure in said space to atmospheric pressure and discharging the non-impregnated solution of wood preservative, (vi) applying a post-vacuum with negative pressure between -600 and -1000 mbar, preferably between -700 and -1000 mbar, more preferably between -800 and -1000 mbar, even more preferably between -850 and -1000 mbar, and at even more more preferably between -850 and -950 mbar, for at least 15 minutes, preferably at least 30 minutes, more preferably at least 45 minutes, even more preferably at least 60 minutes, and even more preferably at least 90 minutes, (vi) discharge of residual non-impregnated solution of wood preservative, where the temperature inside the autoclave is not increased by adding heat energy.

Preferred embodiments of the method are specified in claims 2 to 10.

In a second aspect, wood is impregnated with wood preservative according to the method of any one of claims 1 to 10.

DESCRIPTION OF THE FIGURES

Figure 1: Evolution of pressure in the autoclave and volume of wood preservative solution in the storage tank during the treatment of Red Norwegian

Pines with Tanalith”" Extra.

Figure 2: Evolution of pressure in the autoclave and volume of wood preservative solution in the storage tank during the treatment of Red Norwegian

Pines with Tanatone”".

> BE2021/6069

DETAILED DESCRIPTION

Unless defined otherwise, all terms used in the description of the invention, including technical and scientific terms, have the meaning as commonly understood by those skilled in the art of the invention. For a better appreciation of the description of the invention, the following terms are explicitly explained. "A", "the" and "the" in this document refer to both the singular and the plural unless the context clearly dictates otherwise. For example, "a segment" means one or more than one segment.

When "about" or "around" is used in this document for a measurable quantity, a parameter, a time period or moment, and the like, it means variations of +/-20% or less, preferably +/-10% or less. less, more preferably +/-5% or less, even more preferably +/-1% or less, and even more preferably +/-0.1% or less than and of the quoted value, to the extent that such variations from are applicable in the described invention. However, it should be understood that the value of the quantity using the term "about" or "around" is itself specifically disclosed.

The terms “comprising”, “comprising”, “consisting of”, “consisting of”, “comprising”, “containing”, “containing”, “containing”, “containing”, “containing”, “containing” are synonyms and are inclusive or open terms indicating the presence of what follows, and which do not exclude or preclude the presence of other components, features, elements, members, steps, known or described in the art.

Quoting numeric intervals by the endpoints includes all integers, fractions, and/or real numbers between the endpoints, including those endpoints.

In a first aspect, the invention relates to a method for impregnating wood with a wood preservative, comprising: (1) placing the wood to be impregnated in an autoclave, (i) applying a pre-vacuum, (ii) filling the space under negative pressure with a solution of wood preservative, whereby the negative pressure is maintained, (iii) increasing the pressure and maintaining overpressure in the aforementioned space,

6 BE2021/6069 (iv) lowering the pressure in the aforementioned space to atmospheric pressure and discharging the non-impregnated solution of wood preservative, (v) applying a post-vacuum, (vi) optionally discharging the remaining non-impregnated solution of wood preservative, where the temperature inside the autoclave is not increased by adding heat energy. As used herein, “wood preservatives” are agents that can protect wood against decay, in most cases caused by insects, shipworms, and microorganisms such as molds, fungi and bacteria. Other wood preservatives are fire retardant. Other wood preservatives are water repellent. Wood preservatives can be soluble in water, oils or organic solvents. Examples of wood preservatives contain copper in some form, such as ACC (acid copper chromate), CCA (chromated copper arsenate), ACQ (alkaline copper quaternary), copper azole (CA), and micronized copper. ACQ consist of copper oxide and a quaternary ammonium compound. Copper azole type A (CBA-A) contains copper, boric acid and tebuconazole, type B (CA-B) contains higher concentrations of copper and tebuconazole but no boric acid. Type C contains two synergistic azoles. In micronized copper, the copper is not soluble as a salt, but exists in the form of very small particles, usually copper carbonate. Two types are MCQ (micronized copper quaternary) and MCA (micronized copper azole).

According to a preferred embodiment, the wood preservative is a wood preservative containing a copper complex and an azole. In a more preferred embodiment, the azole is tebuconazole. In another more preferred embodiment, the copper complex is copper ethanolamine complex.

According to a preferred embodiment, the wood preservative solution is an aqueous solution. “Solution” herein also means “suspension” or “emulsion”, with water being the major fraction of the composition.

According to a preferred embodiment, the wood preservative solution has a wood preservative concentration of 4 to 5%W/V.

7 BE2021/6069

In the first step, the wood to be impregnated is placed in the autoclave.

The autoclave comprises an airtight closable chamber for treating wood.

The autoclave preferably comprises a base for supporting the wood in the autoclave. The chassis is preferably slidable or mobile in and out of the autoclave. The autoclave comprises a vacuum pump for creating a negative pressure in the autoclave and a hydraulic system for creating an overpressure.

Furthermore, the autoclave is connected in a lockable manner to a storage tank containing the wood preservative. A pump system ensures that the wood preservative is pumped from the autoclave back to the storage tank side.

The wood is preferably placed outside the autoclave on the sliding or mobile base and pushed or driven into the autoclave. The autoclave is sealed airtight after the wood has been applied.

In a second step, a vacuum is applied for a certain time. In this phase before the actual impregnation under pressure, this is referred to herein as "pre-vacuum". "Atmospheric pressure" herein means the pressure of the free outside air prevailing outside the autoclave. The average atmospheric pressure at sea level (1 atm) is equal to that of a 760 mm column of mercury, being 1013.25 hPa, 1.01325 bar or 1013.25 mbar The prevailing atmospheric pressure generally deviates from this.

In this context, “vacuum” or “negative pressure” means an air pressure that is lower than the prevailing atmospheric pressure. Vacuum is herein expressed in negative pressure values, i.e. as a pressure difference with the prevailing atmospheric pressure. An underpressure of -500 to -900 mbar means at a prevailing atmospheric pressure of 1000 mbar that the absolute pressure in the autoclave is 500 to 100 mbar. An absolute pressure of Ombar is equal to complete vacuum.

In this context, “overpressure” is understood to mean an air pressure that is higher than the prevailing atmospheric pressure. Overpressure is herein expressed in positive pressure values, i.e. as a pressure difference with the prevailing atmospheric pressure. An overpressure of 12500 mbar means at a prevailing atmospheric pressure of 1000 mbar that the absolute pressure in the autoclave is 13500 mbar.

8 BE2021/6069

When the pressure inside the autoclave is set, it is kept constant. By constant pressure it is meant that the pressure varies at most £10%, preferably at most +5%, more preferably at most +3%, even more preferably at most £2% and even more preferably at most +1%.

The negative pressure during the pre-vacuum is between -600 and -1000 mbar, preferably between -700 and -1000 mbar, more preferably between -800 and -1000 mbar, even more preferably between -850 and -1000 mbar, and even more preferably between -850 and -950 mbar.

The duration of the pre-vacuum is at least 5 minutes, preferably at least 10 minutes, more preferably at least 15 minutes, even more preferably at least 20 minutes, and even more preferably at least 30 minutes.

Most preferably, the duration of the pre-vacuum is about 15 minutes.

In a third step, the autoclave is filled under negative pressure with wood preservative from the storage tank. The storage tank is connected to the autoclave in a lockable manner. Due to the negative pressure in the autoclave, the wood preservative will be sucked in as soon as the connection between autoclave and storage tank has been made. It is important that the negative pressure is maintained as well as possible and this at least until the wood is completely submerged in the wood preservative, but preferably until the autoclave is completely filled with wood preservative, i.e. until no free gas phase is present in the autoclave. Maintaining the negative pressure during filling essentially contributes to the high impregnation efficiency of the current method.

In a fourth step, the pressure in the autoclave is increased so that the wood preservative solution is pressed into the wood.

The overpressure during the actual impregnation is at least 10000 mbar, preferably at least 11000 mbar, more preferably at least 11500 mbar, even more preferably at least 12000 mbar, and even more preferably at least 12500 mbar. The overpressure is most preferably between 12500 and 13000 mbar.

The duration of the actual impregnation under pressure is at least 30 minutes, preferably at least 60 minutes, more preferably at least 90 minutes, if

9 BE2021/6069 more preferably at least 120 minutes, and even more preferably at least 180 minutes. Most preferably, the impregnation time is about 180 minutes.

In a fifth step, the pressure in the autoclave is reduced back to atmospheric pressure and the non-impregnated solution of wood preservative is discharged, for example by pumping it back to the storage tank.

In a sixth step, a vacuum is again applied. In this phase, after the actual impregnation under pressure, this is referred to as “post-vacuum”.

The negative pressure during the post-vacuum is between -600 and -1000 mbar, preferably between -700 and -1000 mbar, more preferably between -800 and -1000 mbar, even more preferably between -850 and -1000 mbar, and even more preferably between -850 and -950 mbar.

The duration of the post-vacuum is at least 15 minutes, preferably at least 30 minutes, more preferably at least 45 minutes, even more preferably at least 60 minutes, and even more preferably at least 90 minutes.

Most preferably, the duration of the post-vacuum is 45 minutes.

Finally, in a seventh step, the remaining non-impregnated solution of wood preservative is discharged, for example by pumping it back to the storage tank.

The temperature inside the autoclave is not raised during the whole process by adding heat energy.

According to an embodiment of the method, the wood preservative solution retention is greater than 200 l/m? wood, preferably more than 300 l/m? wood. The retention of wood preservative solution in 1/m?3 of wood is calculated by dividing the net volume of wood preservative (expressed in litres) consumed during the impregnation process by the total volume of wood (expressed in m3) that is in the autoclave. was placed.

According to one embodiment, the retention of wood preservative is more than 10 kg/m? wood, preferably more than 15 kg/m? wood. The retention of wood preservative in kg/m3 wood is calculated by the retention of

10 BE2021/6069 solution of wood preservative in 1/m3 of wood multiplied by the concentration of wood preservative in the solution, expressed in kg/l.

According to another embodiment, the wood moisture content of the wood to be impregnated is between 15 and 25%.

In the context of this document, the wood moisture content (HV%) is the percentage share of the weight of water in the wood relative to the total weight of the wood. The wood moisture content is calculated as:

HV% = — “100%

where mo is the oven-dry mass of the wood and mı is the wet or undried mass of the wood. The oven-dry mass of the wood is determined by drying a test piece of wood in an oven at a temperature of 103°C until the mass of the test piece no longer changes. The mass of the wood after drying at 103°C is the oven-dry mass.

In a second aspect, the invention relates to wood impregnated with wood preservative according to the method of the invention.

In what follows, the invention is described by means of. non-limiting examples which illustrate the invention, and which are not intended or construed to limit the scope of the invention.

EXAMPLES

Example 1: Impregnation of wood with Tanalith'" Extra

A total volume of 8,730 m3? Red Norwegian Pine (RND) cut to various sizes was autoclaved and treated with Tanalith"" Extra wood preservative in a 4.77% w/v aqueous solution (Arxada, West

Yorkshire, UK). The following impregnation program was followed:

Press Press Duration

TP [an gen [emee

We | ash

11 BE2021/6069

Roofs | OO | (a

Ween [ vanen [

Table 1: Pressure development in the autoclave during the impregnation program

The course of the pressure in the autoclave and the volume of solution of wood preservative in the storage tank are shown in Figure 1. It can clearly be seen from the figure that the negative pressure during the pre-vacuum is maintained during the filling of the autoclave with wood preservative. [ou voorasdani (litre)

Table 2: Volume development of wood preservative in the storage tank

The volume of wood preservative solution in the storage tank was 37481 liters before treatment, and 34466 liters after treatment, which amounts to a net usage of 3015 litres. This means a retention of the solution of 345 |/m° or, expressed for 4.77 %w/v of protection agent, 16.5 kg/m° of wood.

Example 2: Impregnation of wood with Tanatone""

A total volume of 9,720 m3? Red Norwegian Pine (RND) sawn to various sizes was autoclaved and treated with Tanatone"" wood preservative in a 4.61% w/v aqueous solution (Arxada, West

Yorkshire, UK). The following impregnation program was followed:

Press Press Duration

TP [ion ge [eme

12 BE2021/6069

Roofs [A vanes [

Pump Out |L [34

Table 3: Pressure development in the autoclave during the impregnation program

The course of the pressure in the autoclave and the volume of solution of wood preservative in the storage tank are shown in Figure 2. It can clearly be seen from the figure that the negative pressure during the pre-vacuum is maintained during the filling of the autoclave with wood preservative. [eoa (liter)

Table 4: Volume development of wood preservative in the storage tank

The volume of wood preservative solution in the storage tank was 36796 liters before treatment, and 33859 liters after treatment, resulting in a net usage of 2937 litres. This means a retention of the solution of 302 |/m° or, expressed for 4.61 %w/v of protection agent, 13.9 kg/m° of wood.

Claims (11)

13 BE2021/6069 CONCLUSIONS CLAIMS 1. Method for impregnating wood with a wood preservative, comprising: () placing the wood to be impregnated in an autoclave, (ii) applying a pre-vacuum with negative pressure between -600 and -1000 mbar, preferably between -700 and -1000 mbar, more preferably between -800 and -1000 mbar, even more preferably between -850 and -1000 mbar, and even more preferably between -850 and -950 mbar, for at least 5 minutes, preferably at least 10 minutes, more preferably at least 15 minutes, even more preferably at least 20 minutes, and even more preferably at least 30 minutes, (ii) filling the autoclave under negative pressure with a solution of wood preservative, the negative pressure being maintained, ( iv) increasing the pressure and maintaining overpressure in said space to at least 10000 mbar, preferably at least 11000 mbar, more preferably at least 11500 mbar, even more preferably at least 12000 mbar, even more preferably at least 12500 mbar, at the most preferably between 12500 and 13000 mbar, for at least 30 minutes, preferably at least 60 minutes, more preferably at least 90 minutes, even more preferably at least 120 minutes, and even more preferably at least 180 minutes, (v) lowering the pressure in said space to atmospheric pressure and discharge of the non-impregnated solution of wood preservative, (vi) applying a post-vacuum with negative pressure between -600 and -1000 mbar, preferably between -700 and -1000 mbar, more preferably between -800 and -1000 mbar, even more preferably between -850 and -1000 mbar, and even more preferably between -850 and -950 mbar, for at least 15 minutes, preferably at least 30 minutes, more preferably at least 45 minutes, even more preferably at least 60 minutes, and even more preferably at least 90 minutes, (vii) discharging residual non-impregnated solution of wood preservative, the temperature within the autoclave not being raised by adding heat energy. 14 BE2021/6069 Method according to claim 1, characterized in that the retention of wood preservative solution is more than 200 l/m3 of wood, preferably more than 300 l/m3 of wood. A method according to claim 1 or 2, characterized in that the wood preservative solution has a wood preservative concentration of 4 to 5% w/v. Method according to claims 1 to 3, characterized in that the retention of wood preservative is more than 10 kg/m3 of wood, preferably more than 15 kg/m3. A method according to any one of the preceding claims, characterized in that the solution of wood preservative is a solution in water. A method according to any one of the preceding claims, characterized in that the wood preservative is a combined wood preservative. A method according to claim 6, characterized in that the combined wood preservative contains a copper complex and an azole. A method according to claim 7, characterized in that the azole is tebuconazole. A method according to claim 7 or 8, characterized in that the copper complex is a copper-ethanolamine complex. A method according to any one of the preceding claims, characterized in that the wood moisture content of the wood to be impregnated is between 15 and 25%. Wood impregnated with wood preservative according to the method of any one of claims 1 to 10.